Adamantane-based epoxy resin and siloxane-modified adamantane-based epoxy resin: Characterization of thermal, dielectric and optical properties

Article abstract of DOI:10.1016/j.reactfunctpolym.2015.04.002

An adamantane-based epoxy resin (ADEP) and a siloxane-modified adamantane-based epoxy resin (Siloxane-ADEP) were synthesized, and their chemical structures were confirmed from FT-IR, ¹H, ¹³C and ²⁹Si NMR spectroscopy measurements. The morphological, thermal, dielectric and optical properties of ADEP and Siloxane-ADEP were studied. The introduction of the adamantane group into the chain of the epoxy resin resulted in improvements in the thermal, mechanical and dielectric properties. These results can be explained in terms of the tricyclic hydrocarbon of the adamantane in a diamond lattice structure and the movement of polymer chains being limited by chair-form cyclohexane rings, resulting in an immobile epoxy structure. Moreover, Siloxane-ADEP exhibited good thermal, mechanical and dielectric properties that were similar to those of epoxy resin, and its better processability may extend its application to electronic packing materials. The UV-Vis transmission spectra revealed that the adamantane-containing epoxy membranes exhibited novel ultraviolet light-filtering properties.

Full text of DOI:10.1016/j.reactfunctpolym.2015.04.002

Reactive & Functional Polymers 91-92 (2015) 11–18
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Adamantane-based epoxy resin and siloxane-modified adamantane-
based epoxy resin: Characterization of thermal, dielectric and optical
properties
a
b,
⇑
c
d
C.W. Tsai , K.H. Wu , C.C. Yang , G.P. Wang
a
School of Defense Science, Chung Cheng Institute of Technology, National Defense University, Taoyuan, Taiwan
Department of Chemical and Materials Engineering, Chung Cheng Institute of Technology, National Defense University, Taoyuan, Taiwan
Chemical Systems Research Division, Chung Shan Institute of Science and Technology, Taoyuan, Taiwan
Office of Research & Development, Ming Hsin University of Science and Technology, Hsinchu, Taiwan
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
An adamantane-based epoxy resin (ADEP) and a siloxane-modified adamantane-based epoxy resin
Received 27 January 2015
Received in revised form 9 April 2015
Accepted 10 April 2015
1
13
(
Siloxane-ADEP) were synthesized, and their chemical structures were confirmed from FT-IR, H,
C
29
and Si NMR spectroscopy measurements. The morphological, thermal, dielectric and optical properties
of ADEP and Siloxane-ADEP were studied. The introduction of the adamantane group into the chain of the
epoxy resin resulted in improvements in the thermal, mechanical and dielectric properties. These results
can be explained in terms of the tricyclic hydrocarbon of the adamantane in a diamond lattice structure
and the movement of polymer chains being limited by chair-form cyclohexane rings, resulting in an
immobile epoxy structure. Moreover, Siloxane-ADEP exhibited good thermal, mechanical and dielectric
properties that were similar to those of epoxy resin, and its better processability may extend its applica-
tion to electronic packing materials. The UV–Vis transmission spectra revealed that the adamantane-
containing epoxy membranes exhibited novel ultraviolet light-filtering properties.
Available online 18 April 2015
Keywords:
Epoxy
Adamantane
Thermal properties
Dielectric properties
Optical properties
Ó 2015 Elsevier B.V. All rights reserved.
1
. Introduction
Epoxy resins, which are one of the most important classes of
Adamantane (tricyclo[3.3.1.13.7]decane) is a highly symmetric
tricyclic hydrocarbon with three fused chair-form cyclohexane
rings in a diamond lattice structure [11,12]. The effects of
incorporating adamantane into backbones or as pendant groups
on the physical, thermal, and mechanical properties of a number
of polymer families have been investigated [13–17]. The incorpora-
tion of adamantane led to superior thermal stability, high glass
thermosetting polymers, have been widely applied in surface-coat-
ing and painting materials, matrices of composites, adhesives,
insulating materials, encapsulating materials, and advanced mate-
rials. With the developments in the aerospace and automobile
industries in the areas of structural composites and adhesives in
microelectronic devices for encapsulating electrical circuit compo-
nents and electronics packaging, excellent properties are required,
including good processability, thermal and chemical resistance,
moisture resistance, superior electrical and mechanical properties,
and good adhesion to many substrates [1–4]. However, the brittle
nature and fire risk of epoxy resins restrict their application in
some advanced fields. To further improve the physical properties
and thermal performance of epoxy resins, researchers have devel-
oped many additives and modifiers, such as calcium carbonate,
adamantane, fullerene, silica, titania and carbon nanotubes [5–10].
g
transition temperatures (T ) and decomposition temperatures,
good mechanical strength, low dielectric constants, and good
transparency. Although the feasibility of incorporating adaman-
tane into the backbone of epoxy resins has been examined [18],
investigations on the relationship of siloxane modification to
physical properties based on adamantane-based epoxy resins are
limited. Silicon-containing compounds can migrate to the surface
of the material during the course of thermal degradation because
of their low surface energy. Their products are silica carbons with
high thermal stability [19]. Silicon carbide can form a protective
silica layer and protect the polymer residue from further thermal
decomposition at high temperatures. The inorganic components
could suppress the production of toxic gases [20].
Epoxy resins are widely used in many fields, such as in the
manufacturing of coatings, adhesives and matrix resins for
⇑
Corresponding author. Tel.: +886 3 3891716; fax: +886 3 3892494.
E-mail address: khwu@ndu.edu.tw (K.H. Wu).
http://dx.doi.org/10.1016/j.reactfunctpolym.2015.04.002
381-5148/Ó 2015 Elsevier B.V. All rights reserved.
1

1
2
C.W. Tsai et al. / Reactive & Functional Polymers 91-92 (2015) 11–18
Br
OH
Br
HO
OH
FeCl3
+
8
0䉝
1,3-bis (4-hydroxyphenyl)adamantine (HPAD)
O
NaOH
Cl CH CH CH
2
2
O
O
H C CHCH2
O
O
CH2CHCH2
OH
O
n
O
CH2CH CH2
2
1,3-bis (4-hydroxyphenyl)adamantane diglycidyl ether (ADGE)
H N(CH ) NH (B210)
2
2 n
2
NH(CH ) NH
NH(CH ) HN
2 n
2
n
HO
OH
OH HO
m
H
H2
2
C
O
O
CH2CHCH2
OH
O
n
O C
Adamantane-based epoxy resin (ADEP)
Scheme 1. Experimental procedure for the synthesis of HPAD, ADGE and ADEP.
advanced composites. Hence, the combinations of adamantane and
polysiloxane with epoxy resins have broader application possibili-
ties. To date, however, there have been few reports on adaman-
tane-based epoxy resins with light-filtering properties. Fang et al.
condenser and an outlet to a beaker containing a solution of
NaOH to capture the HBr released from the reaction. The solution
was stirred at 80 °C for 16 h under nitrogen. The excess phenol
was removed by stirring the product in 500-mL portions of hot
water 3 times, followed by drying under vacuum. The crude pro-
duct was crystallized from methanol to afford 3.04 g (50.7 wt%
yield) of white crystals of HPAD. The experimental procedure is
[
7] prepared fullerene-containing epoxy membranes with tunable
ultraviolet light-filtering properties. However, the thermal, dielec-
tric and optical properties of siloxane-modified adamantane-based
epoxy resins have not been investigated in detail. In this study, 1,3-
dibromoadamantane and phenol were used as the starting materi-
als to prepare 1,3-bis(4-hydroxyphenyl)adamantane (HPAD). Then,
HPAD was reacted with epichlorohydrin to synthesize 1,3-bis(4-
hydroxyphenyl)adamantane diglycidyl ether (ADGE). The synthe-
sized adamantane-based epoxy resin (ADEP) was produced by
curing ADGE with diamine (B210). A novel siloxane-modified
adamantane-based epoxy resin (Siloxane-ADEP) was synthesized
from 3-isocyanatopropyltriethoxysilane (IPTES), phenyltriethoxysi-
lane (PTEOS) and ADGE using the sol–gel copolymerization technique.
The chemical structures of ADEP and Siloxane-ADEP were
1
13
shown in Scheme 1. Fig. 1 presents the H and C NMR spectra
1
of HPAD. H NMR (500 MHz, DMSO-d
(m, 10H, H-1), 2.22 (s, 2H, H-2), 3.43 (s, HOD in DMSO-d
(m, 4H, ArH), 7.22 (m, 4H, ArH), 9.18 ppm (s, 2H, H-6); 13C NMR
(500 MHz, DMSO-d ), d 29.58 (C-4), 35.83 (C-5), 36.36 (C-2),
6
), d 1.72 (s, 2H, H-3), 1.80
6
), 6.75
6
42.28 (C-3), 49.70 (C-1), 115.21 (C-8), 125.78 (C-7), 141.41 (C-6),
155.50 ppm (C-9).
2.2. Synthesis of 1,3-bis(4-hydroxyphenyl)adamantane diglycidyl
ether (ADGE) and ADEP
1
13
confirmed using Fourier transform infrared, H NMR, C NMR
A 100-mL round-bottom flask was filled with 1 g of HPAD,
2
9
and Si NMR spectroscopy measurements. The morphological,
thermal, dielectric and optical properties of ADEP and Siloxane-
ADEP were studied and compared with those of the diglycidyl
ether of bisphenol-A epoxy.
3
.0 mL of isopropyl alcohol and 4.34 g of epichlorohydrin. The reac-
tion temperature was controlled at 80 °C, and 0.625 g of 40 wt%
aqueous NaOH was added dropwise over the course of 1 h. The
mixture was reacted at this temperature for 6 h. After the reaction
reached completion, the salt was filtered, and then the filtrate was
washed three times with water. Then, the organic phase was sepa-
rated from the mixture. Excess epichlorohydrin and the solvent
were distilled using a rotary evaporator to afford 1.97 g of a yellow
liquid of 1,3-bis(4-hydroxyphenyl)adamantane diglycidyl ether
(ADGE). The mixture of ADGE and 10 wt% B210 diamine as a curing
agent was homogeneously dissolved in THF as a solvent. The reac-
tion solution was stirred for 12 h, evacuated for 5 min to remove
the solvent from the solution, and then aged at 60 °C for 48 h to
2
. Experimental
2.1. Synthesis of 1,3-bis(4-hydroxyphenyl)adamantane (HPAD)
HPAD was prepared using a modification of a previously
reported procedure [18]. A 150-mL round-bottom flask was filled
with 1,3-dibromoadamantane (6.00 g), phenol (60.00 g) and
iron(III) chloride (1.10 g). The flask was equipped with a reflux

C.W. Tsai et al. / Reactive & Functional Polymers 91-92 (2015) 11–18
13
polytetrafluoroethylene plate to gel at room temperature for
24 h. The samples were placed in a drying oven at 60 °C for 24 h
to obtain the clear Siloxane-ADEP. The experimental procedure is
shown in Scheme 2. Ep904 resin was prepared in the same way.
The diglycidyl ether of bisphenol-A epoxy used in this work was
supplied by Nan Ya Plastics Co., Ltd., Taiwan, and it possessed an
epoxide equivalent weight of 807 g/eq (Eporite-904). Epoxy resin
and THF were stirred in a 500-mL three-neck round-bottom flask
at 40 °C to obtain the epoxy solution. Then, B210 diamine was used
as the curing agent, and the resulting resin was abbreviated as
Ep904.
(a)
HO
OH
6
1
4
5
3
4
5
3
2
6
2.4. Experimental techniques
The chemical structures were confirmed by Fourier transform
(b)
2
2 6
9
infrared (FTIR) spectral analysis (Tensor 27) of samples prepared
HO
OH
1
13
using the KBr pellet technique. H and C NMR spectra were
recorded on Bruker MSL-500 NMR spectrometers using DMSO-d
as the solvent and tetramethylsilane as the internal standard. The
7
8
6
8
7
5
2
9
Si NMR spectrum of the solid-state sample (MSL-400, Bruker)
was obtained using the cross-polarization/magic-angle spinning
CP–MAS) technique. The morphologies of the samples were
observed using a scanning electron microscope (SEM, Hitachi
S-800) equipped with an energy-dispersive X-ray (EDX) microanaly-
sis system. A PerkinElmer thermogravimetric analyzer (TGA-7)
was used to investigate the thermal stabilities of the samples.
(
3
2
4
9
6
1
5
The samples (ꢁ5 mg) were heated in a N
2
/air atmosphere from
(a)
Fig. 1. (a) 1H NMR and (b) 13C NMR spectra of HPAD in DMSO-d
.
6
1
1
obtain ADEP. The experimental procedure is shown in Scheme 1.
1
1
1
13
1
9
Fig. 2 presents the H and C NMR spectra of ADGE. H NMR
500 MHz, DMSO-d ), d 1.78 (s, H-3), 1.90 (m, H-1), 2.26 (s, H-2),
.68,2.84 (m, H-11), 3.19 (m, H-7), 3.52 (m, H-10), 3.80 (s, H-9),
.83 (s, H-6), 4.27 (m, H-8), 6.92 (m, ArH, H-5), 7.34 ppm (m,
10
6
(
6
ͨ
2
3
1
3
ArH, H-4); C NMR (500 MHz, DMSO-d
C-5), 36.55 (C-2), 42.50 (C-3), 44.20 (C-A), 47.67 (C-1), 49.58 (C-
B), 67.72 (C-C), 69.64 (C-E), 69.86 (C-D), 115.21 (C-8), 126.78(C-
6
), d 29.58 (C-4), 35.83
(
1
4
5
1
ͩ
2
3
7
), 144.31 (C-6), 157.20 ppm (C-9). The H NMR integration ratio
of H-10 and H-11 was higher than that of H-4 and H-5, as shown
in Fig. 2(a). This result may be due to the purification of ADGE
being insufficient and the excess epichlorohydrin not being suffi-
ciently distilled from the product.
(b)
2.3. Synthesis of siloxane-ADEP resin
ADGE (3.0 g) and tetrahydrofuran (THF; 10 mL) were stirred in a
1
00-mL three-neck round-bottom flask at 60 °C to obtain the
8
epoxy solution. Then, IPTES (0.25 g) was added with THF to the
epoxy solution. The entire mixture was homogeneous and was stir-
red at 60 °C until the characteristic peak of the NCO group
7
ꢀ
1
3
(
2270 cm ) in the FT-IR spectrum disappeared. The reaction time
2
was approximately 12 h. A quantitative amount of PTEOS (molar
ratio of 1:1 with respect to IPTES) was placed in a beaker with
4
E
1
0
3
.05 M HNO and deionized water. The resulting solution was
9
6
added to the above-described sol solution, and stirring was contin-
ued under an inert atmosphere at room temperature for an addi-
tional 24 h. Then, B210 diamine was used as the curing agent for
the modified epoxy resin. THF was removed from the siloxane-
modified epoxy in a vacuum oven at room temperature for 1 h,
D
B A
5
C
and then the siloxane-modified epoxy was cast on
a
Fig. 2. (a) 1H NMR and (b) 13C NMR spectra of ADGE in DMSO-d
.
6

1
4
C.W. Tsai et al. / Reactive & Functional Polymers 91-92 (2015) 11–18
Scheme 2. Experimental procedure for the synthesis of Siloxane-ADEP.
(
a)
3
T
(b)
(c)
2
T
(d)
(e)
(f)
-
140 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30
ppm
Fig. 4. 29Si NMR spectrum of Siloxane-ADEP composite.
4
000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm )
Fig. 3. FTIR spectra of (a) DBAD, (b) HPAD, (c) ADGE, (d) ADGE + IPTES, (e)
ADGE + IPTES/24 h and (f) Siloxane-ADEP.
analyzer was used to determine the coefficients of thermal expan-
sion of the samples. The samples were heated in an air atmosphere
from ambient temperature to 100 °C at a heating rate of 5 °C/min.
The dielectric constants of the various epoxy systems were
determined using a Novocontrol GmbH (Germany) dielectric spec-
trometer at room temperature from 100 to 900 MHz. Samples with
a diameter of 10 mm and a thickness of 1 mm were dried in vacuo
at 100 °C until the moisture had been expelled. After cooling to
ambient temperature to 800 °C at a heating rate of 10 °C/min, and
the gas flow rate was maintained at 50 mL/min. Storage modulus
0
(
E ) tests were performed using a dynamic mechanical thermal
analyzer (PerkinElmer DMA-7) with a temperature range from
ambient temperature to 200 °C. A PerkinElmer TMA-7 thermal

C.W. Tsai et al. / Reactive & Functional Polymers 91-92 (2015) 11–18
15
(
(
a)
c)
(b)
1
um
1um
(d)
Si
Si: 11.92 wt%
Si
1
um
(e)
(f)
1um
Si Ka1
Fig. 5. SEM images of (a) EP904, (b) ADEP, (c) Siloxane-ADEP; (d) EDX, (e) Si-mapping and (f) SEM + Si-mapping images of Siloxane-ADEP.
(
a) 100
(b) 100
EP904
EP904
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
90
ADEP
ADEP
Siloxane-ADEP
Siloxane-ADEP
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
200 300 400 500 600
200 300 400 500 600 700
o
o
Temperature ( C)
Temperature ( C)
5
0 100 150 200 250 300 350 400 450 500 550 600 650 700
100 150 200 250 300 350 400 450 500 550 600 650 700
o
o
Temperature ( C)
Temperature ( C)
2
Fig. 6. TGA thermograms of various epoxy systems in (a) N and (b) air.
room temperature, the samples were weighed, placed in 25 °C/
00 °C water for 24 h/2 h, and weighed again according to ASTM
D-570. The moisture absorption was calculated as follows: weight
gain (%) = (W/W
ꢀ 1) ꢂ 100, where W is the weight of the sample
after being placed in water for a certain period and W is the
weight of the sample before being placed in water. Light transmit-
tance measurements of the samples before and after thermal aging
were performed using a UV–Vis spectrophotometer (UV3101PC,
Shimadzu, Kyoto, Japan) over the wavelength range of 300–
800 nm.
1
o
o

1
6
C.W. Tsai et al. / Reactive & Functional Polymers 91-92 (2015) 11–18
Table 1
Physical properties of various epoxy systems.
0
ꢀ6
Sample
Storage modulus E (GPa)
CTE (10 /°C)
Dielectric constant (MHz)
% H
2
O absorption
100 °C
30 °C
200
400
600
800
10 h
168 h
Ep904
ADEP
Siloxane-ADEP
0.24
2.10
0.94
782
24
522
3.63
3.07
4.54
3.61
3.06
4.39
3.64
3.08
4.34
3.85
3.07
4.32
2.23
1.96
2.42
1.99
1.68
2.08
3
. Results and discussion
the cured Ep904 and ADEP exhibited very dense and smooth sur-
faces. As siloxane was introduced, the surfaces become rougher
3.1. Structural and morphological characterization
and exhibited a heterogeneous morphology in the matrix.
Moreover, the EDX spectrum of Siloxane-ADEP indicated the pres-
ence of a significant amount of silicon in the ADEP matrix. As indi-
cated by the SEM and Si-mapping images (Fig. 5(e) and (f)), the
siloxane was uniformly dispersed throughout the ADEP matrix.
This result revealed that Siloxane-ADEP exhibited good miscibility
between the organic and inorganic phases.
Fig. 3 presents FT-IR spectra that provide evidence for the for-
mation of HPAD, ADGE monomer, and Siloxane-ADEP. The charac-
teristic absorption bands of HPAD appeared at 3560 cm (free
ꢀ1
ꢀ
1
ꢀ1
ArAOH), 3200–3500 cm
(ArAOH), 3057/3033 cm
(aromatic
ꢀ1
ꢀ1
CAH), 2915/2845 cm (CAH), 1619/1515 cm (aromatic CAC),
ꢀ
1
and 1242 cm (alkyl–aryl CAC), and the characteristic peak of
ꢀ
1
the CABr group (690 cm ) disappeared. The FTIR spectrum of
3.2. Thermal and mechanical properties
ꢀ1
ADGE exhibited characteristic absorption bands at 1036 cm (aro-
matic CAOAC) and 911 cm (oxirane ring), and the characteristic
absorption peaks at 3200–3500 cm became weak, whereas aro-
matic CAOAC formation and the epoxy group were apparent.
This result indicated that the epichlorohydrin had reacted with
the AOH in HPAD.
ꢀ
1
The thermal stabilities of the various epoxy systems were inves-
tigated using TGA/DTG. The weight loss, as well as various pyroly-
ꢀ1
sis steps up to 700 °C in N and air, are shown in Fig. 6(a) and (b). It
2
was observed that the TGA curves of Ep904 and ADEP exhibited
similar degradation profiles in N , implying a similar mechanism.
2
The characteristic absorption bands of ADGE + IPTES appeared
The incorporation of adamantane into the epoxy resulted in a
ꢀ1
ꢀ1
at 3200–3700 cm (SiAOH) and 2270 cm (N@C@O). Moreover,
retarded mass loss rate and an enhanced char yield. This effect
was attributed to the fact that the rigid and bulky adamantyl ele-
ment increased the rigidity of the epoxy chain, which could
improve the inherent thermal stability of the thermoset substance.
It was observed that the initial thermal decomposition tempera-
tures (250–400 °C) were decreased for Siloxane-ADEP. The initial
mass loss was attributed to the decomposition of aliphatic amine
segments linking the ADEP units to the silica network. The thermal
stability of the graft aliphatic amine segments in Siloxane-ADEP
was lower than that of the backbone aliphatic amine segments in
ADEP, potentially due to hydrogen-bonding effects. This result
may be due to the enhanced heat transfer resulting from the
hydrogen-bonding interaction, which leads to a decrease in the
scission of aliphatic amine segments in ADEP. The weight loss over
the interval of 450–600 °C was attributed to the decomposition of
the adamantane moiety and silica network. A higher char yield
indicated that the introduction of the siloxane favored the forma-
tion of char residue because of the existence of silica in the epoxy
matrices.
the intensity and width of the absorption band at approximately
ꢀ1
3
500 cm significantly increased after the epoxy derivatives were
modified with IPTES oligomer. After condensation (Fig. 3e), the
ꢀ1
intensity of the absorption band at approximately 3500 cm
SiAOH) decreased and the absorption band of the NCO group dis-
appeared. In addition, the intensities of the absorption bands at
(
ꢀ1
ꢀ1
1
730 cm
and 1085/823 cm
increased due to C@O and
SiAOASi stretches. This result indicated that the NCO group in
IPTES had reacted with the AOH in ADGE and that the con-
densation reaction of SiAOH occurred to form a SiAOASi bond.
Siloxane-ADEP was synthesized from ADGE, IPTES, PTEOS, and cur-
ing agent B210. Siloxane-ADEP presented the characteristic silox-
ane and ADEP peaks. This formed connections between the
organic and inorganic phases. There are covalent bonds between
the organic and inorganic moieties. In addition, the OAH stretching
vibrations of the SiAOH and CAOH groups absorb in the region of
ꢀ1
3
200–3700 cm . The absorption characteristics in that region
depend on the degree of hydrogen bonding. Therefore, the inten-
sity and width of the absorption band at approximately
The TGA/DTG curves, recorded in air, of the various epoxy sys-
tems are shown in Fig. 6(b). The major mass loss of epoxy can be
attributed to the breakdown of the hydrocarbon soft segment
phase (300–450 °C) and the hard segment phase (450–550 °C). It
was observed that the thermo-oxidative decomposition tempera-
tures were enhanced for ADEP and Siloxane-ADEP over the interval
of 400–650 °C. This relatively high thermo-oxidative stability can
be explained by the presence of cyclohexane rings and a
ASiAOASiA inorganic network because the bond dissociation
energy of SiAO is higher than that of CAC and CAO. Consistent
with the literature on neat resin systems, the Siloxane-ADEP in this
study was typically more thermally stable than the adamantane-
based epoxy due to the formation of highly crosslinked networks
in the former.
ꢀ1
3
500 cm significantly increased after the epoxy derivatives were
modified with siloxane.
2
9
Si NMR provided structural information regarding the type of
silicon present in the resin network. Fig. 4 presents the 29Si solid-
state NMR spectrum of Siloxane-ADEP. Distinct peaks of the silica
2
network units in the siloxane were observed at ꢀ69.8 (T ) and
3
2
3
ꢀ
2 3
83.6 ppm (T ). T and T denote RASi(OSi) (OH) and RASi(OSi) ,
3
respectively. The results revealed that
T
were the major
microstructures, and formation of the network structure enhanced
the thermal stability and mechanical properties of the epoxy resin.
The compatibility of the organic polymer and siloxane greatly
affects the thermal and optical properties. The morphology of the
fractured surfaces was observed by SEM, and the EDX mapping
technique was used to determine the distribution of silica and
the separation of the microphase in the epoxy matrix. Fig. 5 pre-
sents SEM, EDX and Si-mapping images of the morphologies of
the various epoxy systems. As observed from the SEM images,
0
The storage modulus (E ) and coefficient of thermal expansion
(CTE) were used to evaluate the thermo-mechanical stabilities of
the various epoxy systems, and the results are summarized in
0
Table 1. The E and CTE results were of the order ADEP > Siloxane-

C.W. Tsai et al. / Reactive & Functional Polymers 91-92 (2015) 11–18
17
a)100
(b)100
90
(
90
80
70
60
50
40
30
20
10
0
80
70
60
50
40
EP904
30
ADEP
EP904
Siloxane-ADEP
ADEP
20
10
Siloxane-ADEP
3
00 350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
300 350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
(
c) 100
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
(
a)
b)
(
EP904
ADEP
Siloxane-ADEP
(
c)
3
00 350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
Fig. 7. Transmittance spectra and photographs of the various epoxy systems before/after thermal aging at (a) 90 °C for 24 h (before), (b) 120 °C for 72 h and (c) 120 °C for
68 h.
1
3
.06–3.08 and 4.32–4.54, respectively. The lower dielectric con-
Table 2
stants of ADEP are attributed to the fact that adamantane is a fully
aliphatic hydrocarbon, thus leading to low hydrophobicity and
polarity [21]. On the other hand, the steric hindrance of adaman-
tane decreased the activity of the main chain, and this went against
the orientation polarization of polar groups in the cured epoxy
polymer. It can be observed that the dielectric constants of
Siloxane-ADEP were higher than those of Ep904 and ADEP at all
frequencies. This phenomenon was attributed to the lone pair
electrons of the SiAOH group of the siloxane, which resulted in
the molecule being easily polarized under an electrical field.
The transmittance on 350 and 700 nm wavelength of various epoxy systems before
and after thermal aging.
Samples
Before
90 °C,
68 h
120 °C,
72 h
120 °C,
168 h
1
Transmittance (%)
Ep904
ADEP
350
94
1.9
1.0
700
97
90
350
62
0
700
96
86
350
24
0
700
86
89
350
18
0
700
63
82
Siloxane-ADEP
93
0
89
0
91
0
90
ADEP > Ep904 and ADEP < Siloxane-ADEP < Ep904, respectively.
These results were generally interpreted on the basis of reinforce-
ment of the adamantane cage diamond-like skeleton in the epoxy
matrices, which is able to restrict the motion of the macromolecu-
lar chains. After introducing siloxane into ADEP, the steric hin-
drance in Siloxane-ADEP increased, thereby reducing the
dimensional stability. Moreover, Siloxane-ADEP contains bulky
pendants, which might increase the free volume and reduce the
crosslinking density.
ꢀ
Moisture absorption will ionize ionic impurities (e.g., Cl ) and
consequently corrode integrated circuits. Moisture absorption will
also increase an encapsulating material’s dielectric constant.
Therefore, lower moisture absorption is favorable for encapsulat-
ing materials. Table 1 summarizes the final moisture absorptions
of the three resin films at 100 °C for 10 h and 30 °C for 168 h.
Clearly, ADEP had a lower water absorption (%) compared to
Ep904. Siloxane-ADEP also had excellent moisture resistance
(
2.42%/100 °C and 2.08%/30 °C), but under the same conditions,
the water absorption of ADEP was only 1.96% (100 °C) and 1.68%
30 °C). It is possible to conclude that the waterproofing effect of
3.3. Dielectric and moisture absorption properties
(
the adamantane moiety improved the moisture resistance of the
cured ADEP resin. The higher water absorption of Siloxane-ADEP
compared with Ep904 and ADEP is likely due to the interaction
A lower dielectric constant is one of the most desirable proper-
ties for the next generation of electronic devices. The various epoxy
systems exhibited similar dielectric constants in the frequency
range of 200–800 MHz at room temperature. Table 1 shows the
variations in the dielectric constants as a function of the frequency.
The dielectric constants of ADEP and Siloxane-ADEP were
2
of the SiAOH group and H O (SiAOHꢃ ꢃ ꢃOH
2
), which results in
increased water absorption (%). However, the moisture resistance
properties of Siloxane-ADEP were, in general, satisfactory.

1
8
C.W. Tsai et al. / Reactive & Functional Polymers 91-92 (2015) 11–18
Siloxane-ADEP is soft, resulting in a bendable sample, which means
that it can sufficiently protect encapsulated devices from external
shock.
prepared using the sol–gel copolymerization technique. The
adamantane and siloxane moieties were successfully incorporated
into the epoxy resin system without phase separation. The cured
ADEP and Siloxane-ADEP were superior to epoxy resin in terms
of their thermal and mechanical properties. ADEP and Siloxane-
ADEP had low dielectric constants and low moisture absorption,
and they exhibited little yellowing upon thermal aging at 120 °C
for 168 h under air. The UV–Vis transmission spectra revealed that
ADEP and Siloxane-ADEP exhibited novel ultraviolet light-filtering
3.4. Optical and thermal resistance properties
Fig. 7(a) presents light transmission spectra and photographs of
the three resin films after thermal aging at 90 °C in air for 24 h.
Discoloration was barely distinguishable by the naked eye for all
of the samples. The light transmittance of Ep904 at 350 and
c
properties, and the cutoff wavelength k of these adamantane-con-
7
00 nm was greater than 90%. The light transmittance of ADEP
and Siloxane-ADEP at 350/700 nm was 1.9/90% and 1.0/93%,
respectively. The cutoff wavelengths k of ADEP and Siloxane-
ADEP were 327 and 343 nm, respectively. Here, k was defined as
taining epoxy membranes can be changed simply by varying the
thermal aging temperature. The rigid adamantane structure with
crystalline clusters and charge transfer complexes between the
adamantane derivatives and the epoxy–siloxane composite are
responsible for the UV light-filtering behavior of the adaman-
tane-containing epoxy membranes.
c
c
the wavelength at which the light transmittance was 0.5%. It can
clearly be observed that the spectra ranging from 300 to 350 nm
of ADEP and Siloxane-ADEP showed strong absorptions, and there
was almost no large change in transmittance at 700 nm (>90%).
Interestingly, ADEP and Siloxane-ADEP exhibited novel ultraviolet
light-filtering properties when adamantane was introduced.
Fig. 7(b) and (c) and Table 2 present light transmission spectra
and photographs of samples aged at 90 and 120 °C for 72–168 h
under an air atmosphere in comparison with those of the initial
sample before aging. After thermal aging for 120 °C/168 h, the
transmittance of the Ep904 epoxy decreased with increasing ther-
mal aging temperature and time. However, when the thermal
aging temperature and time were increased, the spectra ranging
from 300 to 400 nm of ADEP and Siloxane-ADEP showed a stronger
absorption and little change in transmittance at 700 nm.
Acknowledgment
The authors thank the Chung-Shan Institute of Science and
Technology for supporting this work (CSIST-0497-V311(102)).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.reactfunctpolym.
2
015.04.002.
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c
Furthermore, the k of ADEP and Siloxane-ADEP exhibited an
almost horizontal bathochromic shift with little change in shape.
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4
. Conclusion
An adamantane-based epoxy resin (ADEP) and a siloxane-modi-
fied adamantane-based resin (Siloxane-ADEP) were successfully